1. Field of the Invention
The present invention is related to a stereoscopic image system and related driving method, and more particularly, to a stereoscopic image system and related driving method for balancing brightness of left-eye and right-eye images.
2. Description of the Prior Art
Three-dimensional (3D) display technology provides more vivid visual experiences than traditional two-dimensional (2D) display technology. In general, the stereoscopic image processing involves two camera systems in which two different images or videos are taken from slightly different camera angles and locations. The object is to simulate the manner in which depth is perceived by a pair of human eyes, which are themselves slightly offset from each other and thus view images at slightly different angles. The two camera images or videos are superimposed as an integrated stereoscopic image and presented to the viewer simultaneously on a television or movie screen. The two camera images are then separated in some fashion for the viewer so that one eye sees only one image and the other eye sees only the other image. In this way, an illusion of depth is created by simulating normal vision. The visual cortex of the human brain fuses this into perception of a 3D scene or composition.
There are two major types of 3D viewing environments: naked-eye and glasses-type. In naked-eye 3D viewing environment, stereoscopic images are directly generated using e-holographic, volumetric, multi-planar or multiplexed 2D display devices and can be viewed without additional devices. In glasses-type viewing environment, 3D viewing devices, such as polarizing glasses, anaglyph glasses, or shutter glasses, are required to creating the illusion of stereoscopic images from planer images.
In a polarized 3D image system, a polarization converting unit or device needs to be disposed in front of a display device or a projector for providing left-eye images polarized in one direction (such as horizontally-polarized) and right-eye images polarized in another direction (such as vertically-polarized). The viewer wears polarizing glasses which also contain a pair of polarizing lenses oriented in the same manner, such as a horizontally-polarized left-eye lens and a vertically-polarized right-eye lens. Since each lens only passes light which is similarly polarized, each eye only sees one of the projected images, thereby achieving 3D effect by creating the illusion of stereoscopic images from planer images.
The polarization converting unit may be a twisted nematic liquid crystal display (TN-LCD) panel or an electrical control birefringence liquid crystal display (ECB-LCD) panel. In a TN-LCD panel or an ECB-LCD panel, the angle or birefringence of liquid crystal molecules is controlled by applying an external field. The light which passed the LCD panel during different display periods may thus be differently polarized. According to the disposition of the polarized units, the TN/ECB-LCD panel has two operational modes: normally-white (NW) mode and normally-black (NB) mode.
FIG. 1 is a diagram illustrating the optical-electrical characteristic of a TN-LCD panel. The horizontal axis represents the voltages applied to the LCD panel, and the vertical axis represents the transmittance of the LCD panel under specific applied voltage. NW represents the characteristic curve of the normally-white mode, and NB represents the characteristic curve of the normally-black mode. In the normally-white mode, the LCD panel with an applied voltage is in the “bright” state which passes light, and the LCD panel without an applied voltage is in the “dark” state which blocks light. In the normally-black mode, the LCD panel with an applied voltage is in the “dark” state which blocks light, and the LCD panel without an applied voltage is in the “bright” state which passes light. Regarding optical characteristics in the “dark” state, the LCD panel may provide a higher contrast due to self-compensation effect in the normally-white mode, while the contrast may be lowered due to leakage caused by light reaction in the normally-black mode. Regarding optical characteristics in the “bright” state, the LCD panel may provide a higher transmittance with a voltage is applied in the normally-black mode. Therefore, the user always perceives left-eye and right-eye images of different brightness, thereby influencing the 3D experience.